Apparatus and method for cutting edge preparation

ABSTRACT

The invention describes an apparatus (1) for a cutting edge preparation of cutting tools (5), in particular of drills or milling tools or similar tools (5), in particular of hard-metal cutting tools, wherein during a relative movement the cutting tool (5) interacts in a machining fashion with a flexibly-bonded grinding body (2) that is provided with abrasive particles, the particles of the grinding body (2) influencing the edge geometry of the cutting tool (5),wherein the grinding body (2) is adapted with its dimensions substantially to the dimensions of the respective cutting tool (5) that is to be prepared and is accommodated in an exchangeable holder (4) which is arranged in a region of a processing device, in particular of a tool grinding machine, and is held such that it is machinable by the cutting tool (5) for the cutting edge preparation. Furthermore, a corresponding method and a corresponding grinding body (2) are given.

The invention concerns an apparatus and a method for cutting edge preparation according to the preamble of claim 1 and a method according to the preamble of claim 16 as well as a machinable grinding body according to the preamble of claim 26.

In a manufacture with machining, for different processing tasks tools are required which achieve high manufacturing accuracy on the component together with a long lifespan in order to ensure economic and competitive product manufacturing of the producing enterprises. In addition to a good wear resistance of the tools, predictable wear behavior is crucial for ensuring high-grade procedural reliability. For the purpose of improving the practice behavior of machining tools, in particular in the field of hard metal tools so-called cutting-edge preparation has been established as an essential process step in the production chain. Herein fine-honing, in particular of the tool cutter, realized after the grinding process for a production of the basic macro-shape of a tool is referred to as cutting edge preparation. Due to the brittle-hard material behavior of hard metals, microscopic defects, like breakout along the cutting edge, are caused by the grinding process. Cutting edge preparation permits remedying such defects as well as creating a cutting edge shape that is adapted to the specific machining process. In many application cases such a load-adapted design of the cutting edge moreover allows augmenting the stability of the cutting edges to such an extent that increased machining volumes can be chosen without loss of service time. As a result, economic efficiency of the production is significantly increasable.

Customary well-known methods for cutting edge preparation, some of which are well-established, are mainly based on methods with a geometrically undefined cutter, like abrasive blasting, magnetic finishing, drag grinding and flow grinding. Beyond these, further separating methods are known, like brushing, spark erosion and laser abrasion as well as the grinding of roundings, for the preparation of cutting edges. The aforementioned methods share the feature that their realization usually requires a special machine or apparatus, which often means high investment costs. These investment costs are a big obstacle, just for small and medium tool-manufacturing enterprises. A further disadvantage in the context of the aforementioned methods is a—sometimes considerable—increase of the throughput time in tool manufacturing. This, on the one hand, results from the additional processing time required for the preparation process. On the other hand, using a separate machine usually requires additional handling efforts. For the sake of completeness it should be mentioned that in the current prior art none of the above-described methods is used for the preparation of reground tools. There being is no opportunity for a preparation of cutting edges in a reground state, these tools generally do not achieve the production quantities of new tools.

Each of the aforementioned methods has specific advantages and disadvantages regarding, on the one hand, the application of the methods themselves but also the resulting shape of edges and surfaces of the tools. Due to their considerable industrial relevance, in the following only these methods will be discussed: abrasive blasting, brushing, drag grinding, grinding, in particular using elastically bonded grinding disks, as well as drill polishing, which is similar to the above methods.

In abrasive blasting a blasting agent, consisting of an abrasive medium and a carrier medium, is accelerated onto the workpiece surface with huge kinetic energy via a blasting nozzle. The abrasive medium is differentiated by grain type, grain size and grain shape. The carrier medium is here often a liquid or air. The most important process influences onto the method are, besides the selection of the blasting agent, the blasting feed rate, the blasting pressure and the blasting angle. The method permits flexible guiding of the blasting nozzle or of the tool that is to be prepared, thus enabling selective processing of individual cutter regions. It is thus in particular suitable for creating complex cutting edge shapes with rather smaller rounding dimensions, wherein selective controlling of material abrasion is quite difficult. In particular in the case of very small tool diameters and with closely-situated cutters, there may be undesired influence on further cutting edges which are not to be prepared, due to so-called passive blasting. This will have a negative influence on process accuracy and/or on the reproducibility of the process result. On the free surfaces and machining surfaces which adjoin the blasted cutting edge and come into contact with the abrasive blast, a characteristic dimpled structure is formed, which usually results in an optical matting of the surface.

A method that is also well established in an industrial context is brushing. The material abrasion is brought about by traversing a rotating brush provided with an abrasive medium along the cutting edge of the tool. The method is suitable for efficient production of rather large and asymmetric roundings. Process-related influencing factors of the method are the cutting speed, the feed rate, the feed motion, the pitch angle of the cutting edge and the brushing duration. Tool-related influences are the thread diameter, the grain size of the abrasive medium, the bristle type and the bristle density. Due to this great number of influencing factors, process controlling is complex and requires accurate knowledge of the method and of the interactions for precisely targeted implementation. In addition to process controlling, process reliability is negatively affected by wear of bristles. In the case of smaller tool diameters, the generation of complex cutter shapes is also limited.

Drag grinding, which is a variant of vibratory grinding, is a method that is also widely used in an industrial context. Material abrasion is brought about by guiding the tools which are to be prepared through a loose, usually resting abrasive medium. Tool movement is herein mostly rotary. Above all, the rotation speed, the rotation direction, the insertion depth, the processing time and the selected abrasive medium are relevant for the processing result. The method permits efficiently creating both small and large roundings. Moreover, considerable improvement of surface quality is obtainable. However, usage also has some disadvantages. Due to the immersion of the tool in the abrasive agent, there is a large contact area of the agent with the tool. In all such contact zones there will be material abrasion, such that selective preparation of individual cutter regions is almost impossible. It is also difficult to adjust formation factors as well and graded roundings and, in particular in the case of shaft tools, in regions with larger diameters considerable material abrasion will be induced by the rotary movement.

Cutting edge preparation may also be realized by a grinding process. Usually a single or double bevel is created along the cutting edge. In a more recent approach more than two bevels are created, thus approximating the profile shape of the cutting edge to a rounding. Beyond this the application of elastically bonded grinding disks is also known in the field of tool preparation. One field of application is the fine-honing of chip flutes of machining tools.

From DE 10 2011 054 276 B4 a method for cutting edge preparation of cutting tools is known, in particular of drills or of milling tools, in particular of hard-metal cutting tools, wherein following a generation of the desired cutting geometry, the cutting tool is first of all adjusted and/or oriented with respect to the required workpiece data of the cutting geometry and/or cutting characteristics, the cutting tool is brought into a rotary movement and is then introduced or bored, while maintaining the rotary movement, into a grinding disk comprising silicon carbide components, tungsten carbide components or diamond components and is flexibly bonded with a rubber-containing bonding agent, to a depth selected depending on the cutting edge geometry and in a position on the circumference of the grinding disk selected for this purpose. Herein a rotating tool is traversed into a grinding disk with a defined drill path and pitch angle. However, as this cinematic can be realized only on a very limited number of machines, the method cannot be considered as a universal preparation method. Moreover, this method does not allow an adjustment of cutting edge roundings extending over the tool diameter. In addition, due to drilling in full material, there will always be considerable rounding of the cutter corner as well as of the transverse cutter, for example in the case of a helical drill, and after comprehensive usage the grinding body will have to be redressed in a complicated fashion. Another disadvantage of this method is in the preparation of tools having large projections, because of the lack of guidance. In this method complex programming needs to be done in order to identify the position of the bore, the pitch angle between a workpiece, in this case the ground machining tool, and the tool, i. e. the grinding disk that is to be machined. Furthermore, after complete circumferential processing, the grinding disk must be brought back to its initial state by methods which must be executed externally. Furthermore, due to the mounting of the grinding disk on a grinding mandrel, grinding disk magazine places are occupied which may possibly be needed.

While it has been proven that cutting edge preparation is an effective means of increasing performance and processing quality of cutting tools, it often requires additional machines and apparatuses. This results, on the one hand, in huge investment costs for such apparatuses, on the other hand in additional workpiece handling costs, which may constitute a decisive portion of the preparation costs in a high-wage country like Germany. The technological and economic aspects mentioned allow deducing the demand for development of a further developed cutting edge preparation method, which is in particular suitable to be used by small and medium manufacturers of machining tools and in which in particular the requirements of low investment costs and operation expenses, simple realization and short tool preparation throughput time are met.

The objective of the present invention is to provide a simple and cost-efficient possibility for selectively preparing cutting edges of rotationally symmetrical machining tools, which in particular have a clamp shaft (shaft tools), in regard to their microscopic shape, while avoiding additional investment costs for machines for the tool-manufacturing enterprise.

The solution of the task of the invention lies in the apparatus according to the characterizing features of claim 1, in the method according to the characterizing features of claim 16 and in the grinding body according to the characterizing features of claim 26, in each case in combination with the features of the respective preamble. Further advantageous implementations of the invention will become apparent from the subclaims.

The invention concerning the apparatus is based on an apparatus for cutting edge preparation of cutting tools, in particular of drills or milling tools or similar tools, in particular of hard-metal cutting tools, wherein during a relative movement the cutting tool interacts in a machining fashion with a flexibly-bonded grinding body that is provided with abrasive particles, the particles of the grinding body influencing the edge geometry of the cutting tool. According to the invention, such a generic apparatus is developed further insofar as the grinding body is adapted with its dimensions substantially to the dimensions of the respective cutting tool that is to be prepared and is accommodated in an exchangeable holder that is arranged in a region of a processing device, in particular of a tool grinding machine, and is held such that it is machinable by the cutting tool for a cutting edge preparation. In contrast to known solutions for cutting edge preparation, the dimensions of the grinding body are in each case adapted to the dimensions, e. g. the circumferential measurements, of the respective cutting tool that is to be prepared, as a result of which on the one hand substantial saving of grinding body material is achievable and, on the other hand, the technological implementation of the cutting edge preparation can be influenced and improved selectively. This requires only as much material of the abrasive material that is to be made into the grinding body as is actually necessary for carrying out the cutting edge preparation, and hence the cutting edge preparation process is realized in an economically efficient manner. Moreover, redressing of large grinding disks, which is otherwise necessary between the respective processes for cutting edge preparation, is dispensed with. Furthermore, the dimensionally adapted grinding body is accommodated in a corresponding exchangeable holder, which is arranged, for example, in the workroom of a tool grinding machine and is held such that it is machinable by the cutting tool for cutting edge preparation. On the one hand, the exchangeable holder enables a furnishing of the holder with respectively new or different grinding bodies independently from the basic processing, e. g. in the grinding machine, thus substantially decoupling the re-furnishing of the grinding bodies from the actual processing. On the other hand, the dimensionally adapted grinding body may be accommodated—in a manner that is especially space-saving and thus hardly interferes, for example, with a possible upstream grinding process on the tool grinding machine—e. g. in the workroom of the grinding machine, and may be kept available for an execution of the cutting edge preparation. This substantially facilitates and decomplicates, after the basic grinding of the cutting tool on the tool grinding machine, an execution of the cutting edge preparation on the same tool grinding machine, ideally in the same clamping arrangement, as no or only little additional equipment is required, e. g. at the tool grinding machine, such additional equipment taking up only little or no additional space in the workroom of the tool grinding machine. It is hence also for small tool grinding outfits possible to offer not only basic tool grinding but also cutting edge preparation without the necessity of investing in expensive add-on devices for the tool grinding machine or of acquiring additional machines. However, it is of course also possible to apply and to constructionally provide the apparatus also for processing devices other than a tool grinding machine, for example for drilling machines, turning machines or the like, for universal as well as for special machines, on which cutting tools that are to be prepared are processed or used and on which the cutting edge preparation may then be carried out close to the process or depending on requirements in order to ensure defined cutting conditions. The apparatus for cutting edge preparation may also be used on any device, in particular any processing device, which enables a relative movement between a cutting tool and a grinding body and on which a cutting edge preparation may be executed as well. In this light, the denomination of the processing device shall be considered to be general and not limiting. If the application of the apparatus on a tool grinding machine is discussed here by way of example, other processing devices or general devices are always also implied and comprised.

A particular advantage is given if the exchangeable holder is held in the workroom of a tool grinding machine, preferably such that it is insertable in a grinding disk receptacle of the tool grinding machine. The construction space of the grinding disk receptacle is a region of the grinding disk receptacle that has normally no functional use and is usually arranged in a prolongation of the clamping cone or of a similar clamp receptacle in the region that is encompassed by the disk-shaped grinding disk. This collar, which the grinding disk is plugged onto, is usually embodied of a full material and is not used otherwise. Therefore, it is just this space, which is arranged centrally in the workroom of the tool grinding machine, that can now be used to form a fitting-in space for the exchangeable holder with the grinding body, in which the grinding body is held for being machined by the cutting tool for cutting edge preparation. Hence in such an arrangement of the grinding body, which is small in regard to construction volume and is adapted to the dimensions of the cutting tool, no additional construction space is required for the cutting edge preparation; and the cutting edge preparation can moreover be carried out in a region of the workroom of the tool grinding machine that is easily accessible and does not require any change of the cinematic for the movement of the grinding disk or of the cutting tool. However, it is of course also conceivable to arrange the grinding body, which is small in regard to construction volume and is adapted to the dimensions of the cutting tool, in a different place in the workroom of the tool grinding machine. Such a position may be situated, for example, in the workroom of a tool grinding machine, in particular in the region of the grinding spindle, or in a different position. There may also be a variant implemented as a space-saving pallet system, in which the afore-described exchangeable holders, together with the grinding bodies, are kept available with identical or differing diameters in a magazine. In this way an interaction is enabled between the tool that is to be produced and the grinding body for a plurality of ground tools. The apparatus that is realizable as a pallet may be implemented to be round, square or rectangular, and may—depending on dimensions—accommodate a certain number of exchangeable holders together with the grinding bodies. It is also conceivable to provide the exchangeable holder in motion devices like spindles of other processing devices, for example on the work spindle of a turning machine or the like.

It is also advantageous if the grinding body is implemented substantially in a cylindrical fashion. As the cutting tools which are to be prepared usually also have at least principally cylindrical dimensions, a cylindrical implementation of the grinding body allows achieving a large extent of adaptation to dimensions and shapes of the cutting tools, as a result of which considerable saving of abrasive material of the grinding body is achievable in the context of the dimensional adaptation of the measurements of the grinding body to the measurements of the cutting tools For this purpose, in a further implementation the cylindrical circumferential measurements of the grinding body are substantially adapted to the circumferential measurements of the cutting tool that is to be prepared, such that in the course of the—usually several—cutting edge preparations of cutting tools which are to be processed one by one, the grinding body can be machined successively and more or less completely, and therefore no unused residue of the abrasive material needs to be disposed of.

It is furthermore of essential advantage that after complete usage, the grinding body can be simply replaced by a new grinding body. As a result, times taken for processing a cutting tool will be prolongated only slightly, and the cutting edge preparation does not unnecessarily prolongate the time required for producing the cutting tool by otherwise necessary refitting or the like.

In the first implementation the grinding body is simply arranged exchangeably in the exchangeable holder, and is preferentially pressed into the holder. For this purpose, the rotationally symmetrical grinding body may for example be manufactured and pressed into the exchangeable holder with a very slight allowance that is adapted to the diameter of the cutting tool that is to be prepared. As a result of the fitting-in, an easily producible and sufficiently rotationally fix connection is established between the grinding body and the exchangeable holder so as to securely receive the processing forces during cutting edge preparation.

In a particularly advantageous implementation, it is conceivable that the exchangeable holder is realized in such a way that it is insertable into a, preferably central, bore in the grinding disk receptacle, preferably in the receiving collar of the grinding disk. This easily accessible volume, which has up to now been mostly unused as was described above, can be provided with almost any tool grinding machine by a simple modification of a customary grinding disk receptacle at a machine-side tensioning element for the grinding disk, while changing the workroom of the tool grinding machine not at all or only in an insubstantial manner. It is possible in this aspect as well to provide a suitable fitting-in space for inserting the exchangeable holder on other processing machines, like in a spindle of a turning machine or a similar processing device.

In a further implementation the exchangeable holder may comprise an outer thread, which can be screwed into the bore in the grinding disk receptacle that is provided with an inner thread. In this way the exchangeable holder may be fitted and secured in the bore in the grinding disk receptacle in a close-fitting and quick manner. However, it is also conceivable to press or insert the exchangeable holder into a, preferably central, bore in the grinding disk receptacle and to hold it there in a rotationally fix fashion, e. g. by something like a bayonet or a clamping or the like.

In particular for a cutting edge preparation of long-projecting cutting tools having a large length:diameter ratio, a guide bushing may be arranged in the region of the exchangeable holder for the grinding body, such that long-projecting cutting tools, when guided via the guide bushing, can be prepared and thus processed more accurately and more safely than without additional guidance. Such long-projecting cutting tools may, for example, be asymmetrical deep-drilling tools, deep-hole drills, helical drills or the like, with a large length:diameter ratio, which otherwise tend to deviate when processed or tend to vibrations during cutting edge preparation because of their length. For this purpose, in a further implementation the guide bushing can be arranged relative to the exchangeable holder—preferably on the exchangeable holder in a prolongation of the exchangeable holder—in such a way that the guide bushing guides and supports the long-projecting cutting tool in front of the region of the machining of the grinding body.

It is also conceivable that electrical conductor paths and/or sensor elements, which provide information on the progression of the cutting edge preparation, are introducible in the exchangeable holder. For example, it is additionally possible that the course of processing is monitored and if applicable influenced during the cutting edge preparation by means of touch-free sensors or the like. In a further implementation it is conceivable that for a voltage supply the sensor elements are equipped with accumulators, which are integrated in the exchangeable holder and can be charged in the grinding disk magazine or externally while not in use. This allows, in non-productive times in which the exchangeable holder is not in use, to have sufficient energy stored in the accumulators so as to enable an execution of the above-mentioned monitoring processes during the cutting edge preparation, when the respective exchangeable holder has been exchanged.

A special advantage is provided if the grinding body comprises abrasive particles, which are in particular implemented of silicon carbide, aluminum dioxide or diamond, and is successively completely machined by the cutting tools which are to be prepared. The machining behavior of the grinding body, and thus the achievable cutting edge preparation, can be influenced over a wide range of possibilities by the selection or mixture of the abrasive particles which are respectively made into a grinding body as well as, in a further implementation, by mixing fine and/or coarse abrasive particles. It is herein also conceivable to implement the distribution of fine and/or coarse abrasive particles inhomogeneously withing the grinding body, for example in order to induce different preparation behavior, for example in the core region and the peripheral region of the grinding body, thus allowing different preparation results in individual regions of the cutting tool in adaptation to a respective geometry of the cutting tool that is to be prepared.

It is furthermore conceivable that the grinding body has an axially-extending perforation, which is adapted to the cutting tool diameter and within which the cutting tool is not affected by the particles of the grinding body. Thus it is advantageous, e. g. in the cutting edge preparation of drills, to prepare the region of the transverse cutter of the drill not at all or differently than the region of the main cutter. If, due to the perforation, there is no grinding body material present just in the region of the transversal cutter, the region of the transversal cutter will not be changed.

Beyond this it is conceivable that the grinding body comprises sections having differing degrees of hardness of the bonding, in particular radial annulus-shaped sections having differing degrees of hardness. The bonding of the abrasive particles of the grinding body has a direct effect on the machining behavior of the grinding body and therefore on the local cutting edge preparation of the cutting tool. By differing hardness or by regions having different hardnesses of the bonding, a further adaptation of the result of the cutting edge preparation to the requirements of the respective cutting tool is achievable. For example, the core of the grinding body may have a higher hardness of the bonding than the peripheral region in order to obtain a regular cutting edge rounding due to the elastic deformation of the rotationally symmetrical grinding body.

The invention moreover concerns a method for cutting edge preparation of cutting tools, in particular of drills or milling tools or similar tools, in particular of hard-metal cutting tools, wherein during a relative movement the cutting tool interacts in a machining fashion with a flexibly-bonded grinding body which is provided with abrasive particles, the particles of the grinding body influencing the edge geometry of the cutting tool, i. e. a method in which the grinding body is adapted with its dimensions substantially to the dimensions of the respective cutting tool that is to be prepared, and is accommodated in an exchangeable holder, which is arranged in the region of a processing device, in particular a tool grinding machine, for example in the workroom of a tool grinding machine or of a different processing device, and in which the grinding body is successively completely machined by the cutting tools that are to be prepared. Essential characteristics and advantages of the method are directly connected to the apparatus described and explained above, hence the described characteristics and advantages of this apparatus may be referred to for a characterization of the method according to the invention.

A special advantage is also given if the cutting edge preparation can be carried out in the same clamping arrangement, directly following a first-time manufacturing of the shape of the cutting tool or following a regrinding of the cutting tool, on the same processing device, for example a tool grinding machine, or an a different processing device. In this way it is possible, on the one hand, to do without additional devices for a separate cutting edge preparation, which would otherwise be necessary, and also to carry out the cutting edge preparation directly in the same clamping arrangement and on the same tool grinding machine or processing device which the basic shaping of the cutting tool is executed on. The cutting edge preparation can moreover be also carried out after regrinding of an already-used cutting tool, thus benefiting from the advantages of the cutting edge preparation for these reground cutting tools as well.

It is especially advantageous that in the machining of the grinding body a wide range of adaptation of the cutting speeds is obtainable by the relative movement of grinding body and cutting tool, in particular by the superimposition of the rotation directions and rotation speeds. Many parameters of the cutting edge preparation are affected by the cutting speed of the cutting edge preparation and may therefore be used selectively with a large variety of possible cutting speeds for a controlling of the results of the cutting edge preparation.

It is furthermore conceivable that the grinding body and/or the cutting tool execute rotary movements during the machining of the grinding body. Besides the usual rotation of the cutting tool, the grinding body is also capable of rotating, if applicable counter-rotating or rotating with different rotation speeds. In this way, in particular by the superimposition of the rotary movements of the grinding body and/or of the cutting tool, roundings and/or tiltings of the cutting edge of the cutting tool can be selectively induced, or a production of asymmetrical cutting edge profiles and/or of cutting edge profiles which are variable over the tool diameter may be enabled.

Beyond this it is conceivable that during the cutting edge preparation only the cutting tool that is to be prepared executes the necessary translational and rotary movements.

It is also conceivable that the grinding body has sections with different degrees of hardness of the bonding and thus creates variable roundings over the cutting region of the cutting tools. It is possible, for this purpose, to produce the grinding body selectively with locally or section-wise variable degrees of hardness of its bonding, such that it is adapted to the respective cutting tool that is to be prepared, thus influencing the local machining by the cutting tool and thus the local cutting edge preparation.

It is further conceivable that due to an axially-extending perforation, which is adapted to the cutting tool diameter and within which the cutting tool is not affected by the particles of the grinding body, the grinding body subjects only defined regions of a cutting tool, in particular for example the main cutters of a drilling tool, to a cutting edge preparation while other regions, in particular the transverse cutter of a drilling tool, are not rounded.

The grinding body may also have external measurements which are adapted to the cutting tool diameter, such that only selected regions of the cutters of the cutting tool are subjected to a cutting edge preparation.

For certain cutting tools that are to be prepared it is conceivable that the cutting tool having main cutters and secondary cutters, in particular milling tools, frictional tools and/or sequential-drilling tools, successively machines—by means of its main cutters, respectively secondary cutters—respectively corresponding grinding bodies which have different characteristics. Herein, for example, the main cutters of a reamer may be prepared by means of a grinding body that is differently shaped or dimensioned than a grinding body for the secondary cutters, thus obtaining in each case the optimum preparation result for the main cutters, respectively the secondary cutters.

The invention further concerns a grinding body for an execution of the method according to claim 16, wherein the cylindrical circumferential measurements of the grinding body are substantially adapted to the circumferential measurements of the cutting tool that is to be prepared.

A particularly preferred embodiment of the apparatus according to the invention is shown in the drawing.

It is shown in

FIG. 1 in a principle-fashion illustration: the basic construction and the function of an apparatus according to the invention, arranged in the grinding disk receptacle of a grinding disk before the cutting edge preparation of a drill,

FIG. 2 an apparatus according to the invention as shown in FIG. 1, with an additional guide bushing before the cutting edge preparation of a long-projecting deep hole drill,

FIG. 3a-3c views and sections through differently implemented grinding bodies of the apparatus according to the invention of FIG. 1,

FIG. 4a-4d detailed sectional views of the exchangeable holder and grinding bodies arranged therein, for the cutting edge preparation of different cutting tools,

FIG. 5 a pallet-like magazine at an apparatus according to the invention, with places for receiving a plurality of exchangeable holders and grinding bodies arranged therein.

In FIG. 1, in a principle-fashion illustration the basic construction and the function of an apparatus 1 according to the invention can be perceived, the apparatus 1 being exemplarily arranged in the grinding disk receptacle 3 of a grinding disk 4 before the cutting edge preparation of a cutting tool 5, which is in the present case embodied as a drill. The apparatus 1 is arranged on a customary tool holder, which is in the present case implemented as a cone-shaped receptacle 19 of a grinding disk 14, of the kind usually used in customary tool grinding machines. The actual implementation of the tool-grinding-machine-side receptacle of the apparatus 1 is herein not relevant and may comprise any kind of mechanical interface with the tool grinding machine. Arrangements of this type may also be realized on other processing devices, like for example drilling machines, turning machines or other devices of that kind. The embodiment of the tool grinding machine shown in the figures is herein only to be seen by way of example and may be implemented in multiple modifications.

On the cone-shaped receptacle 10 in the workroom of the tool grinding machine, a receiving collar 3 is arranged for receiving the grinding disk 14, on which the grinding disk 14 is plugged with its perforation and is then secured in a customary manner by a cap nut 9 via a thread 8. This receiving collar 3 is usually made of a full material and has no further task besides supporting the grinding disk 14.

According to the invention, a portion of the receiving collar 3 which is otherwise made of a full material and which is situated centrally in the work region of the tool grinding machine, is used for an accommodation of the apparatus 1 according to the invention. For this purpose, from the work region of the tool grinding machine a central longitudinal bore 11 is introduced into the receiving collar 3 as a blind bore, which a sleeve-like, easily exchangeable holder 4 for a grinding body 2—that will be described in detail below—can be inserted in. As a result of this arrangement of the apparatus 1, the apparatus 1 will not encumber normal operation of the tool grinding machine while providing the receptacle for a grinding body 2, which may be used for the cutting edge preparation of a cutting tool 5.

The exchangeable holder 4 has such an outer diameter that it is insertable into the longitudinal bore 11 of the receiving collar 3 in a largely tolerance-free manner. A fixing of the exchangeable holder 4 in the longitudinal bore 11 can be brought about by an end-side thread 6 on the outer surface of the exchangeable holder 4, which can be screwed into a corresponding counter-thread in the longitudinal bore 11. It would also be conceivable to fix the exchangeable holder 4 in the longitudinal bore 11 by pressing-in or in another form-fit or force-fit manner if, on the one hand, a rotationally fix fixation is ensured with easy exchangeability of the exchangeable holder 4.

In the interior of the sleeve-like structured exchangeable holder 4 there is also a bore 23 that a cylindrical grinding body 2, which may be used for an interaction with the cutters 7 of the cutting tool 5 in the context of the cutting edge preparation of the cutting tool 5, can be inserted into or pressed into in a rotationally fix fashion. The grinding body 2 is implemented of a flexibly bonded abrasive-particle matrix, for example of rubber-like bonded abrasive particles which are made of hard materials.

In regard to its cylindrical outer measurements, the grinding body 2 is adapted to the circumferential measurements of the cutting tool 5, in the present case the outer diameter of the drill, and has an outer diameter that is slightly greater than the outer diameter of the cutting tool 5, such that in the cutting edge preparation the cutters of the cutting tool 5 in any case come into contact only with the grinding body and not with the exchangeable holder 4.

In order to carry out the cutting edge preparation of the cutting tool 5, for example after basic grinding of the tool shape by means of the grinding disk 14, the cutting tool 5 that is embodied as a drill is positioned, in the longitudinal bore 11 of the receiving collar 3, in front of the apparatus 1 in such a way that the axis of the cutting tool 5 and the longitudinal bore 11, and thus the exchangeable holder 4, are in alignment with one another. The cutting tool 5 is then—during a relative rotation between the cutting tool 5 and the grinding body 2—advanced to the grinding body 2 in the feed direction until the cutters of the cutting tool 5 interact in the designated manner with the grinding body 2, machining the grinding body 2 and being thus prepared. Herein the grinding body 2 is machined at least section-wise and is thus shortened in a longitudinal direction. Following the cutting edge preparation of the cutting tool 5, the cutting tool 5 is re-traversed out of the exchangeable holder 4 against the feed direction 24 and is ready for removal.

The process may then be repeated with the subsequent cutting tool 5, as a result of which the grinding body 2 is more and more machined away successively and, upon reaching a use-up limit, must be replaced. For this purpose, the entire exchangeable holder 4 containing the remainder of the grinding body 2 is removed out of the longitudinal bore 11 and is replaced by a exchangeable holder 4 that has been pre-equipped with a new grinding body 2. Due to the quick exchangeability of the exchangeable holder 4 containing the grinding body 2, work can be continued directly. Further exchangeable holders 4 of the same type may, for example, be stored in other grinding disk receptacles as a depot, to be used if the preparation remains the same. This allows delaying the replacement of the grinding body 2 until the job has been finished or until the wear limits of the grinding disks 14 have been reached.

In FIG. 2 a modified apparatus 1 as shown in FIG. 1 is illustrated, which has been modified for a cutting edge preparation of a long-projecting cutting tool 13, in particular a deep hole drill. As in a grinding process and also during cutting edge preparation, such long-projecting cutting tools 12 tend to get pushed sideways and to start vibrating, the cutting tool 13 is in this case guided and supported by a guide bushing 12 that is arranged at a front side of the exchangeable holder 4, thus avoiding or substantially avoiding the negative effects of the long projection.

FIGS. 3a to 3c present views and sections through differently-structured grinding bodies 2 of the apparatus 1 according to the invention of FIG. 1, which constitute, by way of example, conceivable modifications of the grinding body 2.

In FIG. 3a a grinding body 2 may be perceived of the kind shown in FIG. 1, which is implemented homogeneously over the entire machining region of the grinding body 2.

FIG. 3b shows a grinding body 2 having a central perforation 15, which may be used for example for the cutting edge preparation of a drill as a cutting tool 5. The drill then does not interact with the grinding body 2 in the region of the perforation 15 as there is no abrasive material in this region. As a result, the cutting tool 5 embodied as a drill is not affected in the region of the sensitive transverse cutter and keeps the shape achieved by the preceding grinding process with the grinding disk 14. Due to the sleeve-like shape of the grinding body 2, the main cutters are prepared only in the region of the main cutters.

It is also conceivable, as shown in FIG. 3c , that the peripheral region 17 and the core region 16 of the grinding body 2 are made of different abrasive particles or of identical abrasive particles having different bonding hardness and thus different machining characteristics. For example, the core region 16 of the grinding body 2 may have a higher bonding hardness than the peripheral region 17 in order to achieve a minimization of elastic deformations at the inner cutter of the cutting tool 5. Herein a plurality of modifications of the grinding body 2 are conceivable, depending on the cutting tool 5 that is to be prepared and its shape.

In FIGS. 4a to 4d detailed sectional views are shown of the exchangeable holder 4 and of grinding bodies 21, 22 for the cutting edge preparation of different cutting tools 18, 19 and 20, which are arranged in the exchangeable holder 4. All the tools 18, 19 and 20 have in common that they have different primary cutters and secondary cutters which are to be prepared and which can be prepared neither in a simple manner nor in a single run.

For example, the reamer 18 shown in FIG. 4a can be prepared using the subregion 22 of the grinding body 2 on the primary cutters and simultaneously using the subregion 21 of the grinding body 2 on the secondary cutters. It is however also conceivable, as is shown in FIG. 4b , to prepare the secondary cutters in an individual processing, following the preparation of the primary cutters, using only the subregion 21 of the grinding body 2 on the secondary cutters.

In FIG. 4c the cutting edge preparation of a sequential drill 19 is shown, whose two steps are prepared simultaneously on two subregions 21 and 22 of the grinding body 2 which are, for example, bonded in different manners.

FIG. 4d shows a cutting edge preparation of a milling tool 20 on the secondary cutters only, which interact with a subregion 21 of the grinding body 2.

FIG. 5 shows a conceivable implementation of a pallet-like magazine 25 at an apparatus 1 according to the invention, with receptacles 26 for receiving a plurality of exchangeable holders 4 and of grinding bodies 2 arranged therein. The exchangeable holders 4 with the grinding bodies 2 may be kept available in such a pallet-like magazine 25 with identical diameters or with differing diameters. This allows simple and automatizable exchanging of the exchangeable holders 4 with the respectively required grinding bodies 2, thus enabling a quick automatizable interaction between the respective cutting tool 5 that is to be produced and the suitable grinding body 2 for a plurality of ground tools 5. The device that is here implemented exemplarily as a pallet-like magazine 25 may be realized so as to be round, square or rectangular, and may provide a certain number of receptacles 26 for exchangeable holders 4 with grinding bodies 2, depending on respective measurements.

In the following essential characteristics and advantages of the invention will be briefly explained:

The basic idea of the method according to the invention is the usage of a flexibly-bonded grinding body 2 implemented of abrasive particles, which is here exemplarily installed in a specifically developed grinding disk receptacle 3. In the defined machining of such a grinding body 2, material abrasion will occur on the cutting edge of the cutting tool 5, which may be used for a selective preparation. This method is carried out, for example, on a customary tool grinding machine and can thus be integrated at the end of the process chain for tool production, respectively for tool regrinding, without additional handling efforts. The material abrasion that is necessary for the preparation is generated by the relative movement between a grinding body 2 and a cutting tool 5. The cylindrical grinding body 2 is herein, for example, clamped in the grinding disk receptacle 3 in a positionally fixed manner while the necessary translational and rotary movements are executed by the cutting tool 5 that is to be prepared.

Furthermore, due to deliberate superimposition of the rotational directions of the cutting tool 5 and the grinding disk receptacle 3, there is in this case a possibility of selectively adjusting roundings and tiltings of the cutting edge. It is further possible, due to a construction of the grinding body 2 with different degrees of hardness, to create variable roundings over the cutter region of the cutting tool 5. A well-known problem is the rounding of the transverse cutter of the cutting tool 5 brought about by established preparation methods. The usage of a grinding body 2 having a perforation 15 that is adapted to the tool diameter 5 provides possibilities of adapting the main cutters, for example of a drilling tool 5, to the preparation process while avoiding a rounding of the transverse cutter. The same applies in regard to the accurate adaptation of the diameter of the grinding body 2 to the diameter of the cutting tool 5 that is to be prepared.

Beyond this, due to the free process cinematic, there are further fields of application, like for example the preparation of reamers, micro-milling tools and sequential drilling tools.

The machining of the grinding body 2 results in a material abrasion on the cutting edge of the cutting tool 5, which is thus rounded. The advantage of the method according to the invention lies in that the tool production (grinding of the macro-shape) and a defined generation of the microscopic cutting edge shape can be carried out, for example, on the same tool grinding machine or processing device. Due to the machining of the grinding body 2, new abrasive medium will always be available, as a result of which there are constant preparation conditions for the duration of the process. Influencing of the tools is herein limited to those regions of the cutting tool 5 that come into contact with the grinding body 2, which constitutes an advantage with respect to other preparation methods, like drag grinding or abrasive blasting. In addition to the low investment costs, preparation costs per tool are small as the exchange of grinding bodies 2 can be brought about in a quick and simple manner.

With the current state of the art, in particular the cutting edge rounding of long-projecting cutting tools 13 having a high length:diameter ratio (l/d ratio) requires special handling and extensive process controlling if a suitable cutting edge preparation is to be realized. The apparatus according to the invention offers the potential of enabling a preparation of such long-projecting cutting tools 13 by the simple cinematic and by processing in one clamping arrangement and within existing production procedures on the tool grinding machine or processing device in a short time. However, besides cutting tools 13 having a high l/d ratio customary rotationally symmetrical machining tools may also be prepared by the present method with a slight modification of the grinding bodies 2.

In addition to the cutting edge rounding of new tools 5, the method according to the invention also enables a preparation of cutting tools 5 which were reground and are therefore already coated with a hard-material layer on certain functional surfaces. According to currently available knowledge, this cannot be selectively realized by currently available methods, such that the performance of reground cutting tools 5 is mostly significantly lower than the performance of new cutting tools 5.

For the implementation of the apparatus 1 according to the invention, the accommodation of the exchangeable holder 4, for example in the grinding disk receptacle 3, is crucial. The grinding disk receptacles 3 normally used on tool grinding machines have corresponding interfaces to the tool grinding machine spindle. These are usually embodied as hollow-shaft cones (HSK), shaft cones (SK) or as a further, mostly standardized, interface in order to permit high flexibility and precision with the grinding disk exchange. Herein for a tool grinding, the grinding disks are usually put upon a mandrel 3, having for example a diameter d=20 mm, they are positioned by means of distance rings and are fixed via a clamping nut 9. The core of the mandrel 3 has not had any function up to now. Fitting-in the exchangeable holder 4, in the present case into a bore 11 having an inner thread, provides the mandrel 3 with an additional functionality and the grinding disk receptacle 3 is considerably upgraded in regard to its utilizability. Besides the fixation of the exchangeable holder 4 the connection, which can be screwed or can be joined otherwise, might also permit an implementation of further functional elements which are not involved in the cutting edge preparation. Moreover, corresponding receptacles could be provided on other processing devices, for example on turning machines, drilling machines, or other specifically or universally applicable devices.

The grinding bodies 2 developed specifically for the application in the cutting edge preparation have an elastic bonding of the abrasive particles with a degree of hardness that must be defined depending on the respective application case. This is a rotationally symmetrical grinding body 2 containing fine or coarse abrasive particles, for example silicon carbide, aluminum dioxide or diamond, which is successively completely machined by the cutting tools 5 which are to be prepared. The rotationally symmetrical grinding bodies 2 are herein adapted to the diameter of the cutting tool 5 that is to be prepared; they are produced with a very small allowance and are pressed into the exchangeable holder 4. In this way rounding of the exposed cutter corners of the cutting tools 5 can be avoided or can be significantly minimized in comparison to existing methods. It is possible, besides the rotationally symmetrical base bodies having a defined bonding hardness, to produce grinding bodies 2 which have different degrees of hardness and are thus correspondingly adapted to the application case and to the diameters that are to be processed. In this context in particular the possibility may be mentioned that with the cutting tools 5 it may be necessary that the core 16 of the grinding body 2 has a higher hardness than the peripheral region 17 in order to obtain a regular cutting edge rounding due to the elastic deformation of the rotationally symmetrical grinding body 2.

Furthermore, the process cinematic offers additional possibilities of covering a wide range of parameters in regard to the cutting speeds when machining the grinding body 2, for example by the superimposition of the rotation directions and rotation speeds, independently from the performance capability of the workpiece spindle and of the tool spindle. Moreover, by differently oriented, counter-directional and co-directional movements of the grinding disk receptacle 3 with the integrated grinding body 2 and the cutting tool 5, influences regarding the cutting edge tilting, of form factor K, may be enabled and adjusted. By way of the introduction of perforations 15, the introduction of cores 16 having different hardnesses, abrasive particles and grain sizes, and the flexible shaping of the grinding bodies 2, this method provides an opportunity of a transfer to a great number of further variants of machining tools 5. Beyond this, superimposition of the axes of the grinding disk receptacle 3 allows developing and realizing a different cinematic which approximates a milling processing, thus enabling a preparation of different milling tools selectively in regard to front cutters and/or circumferential cutters.

In addition to the afore-described usage for grinding bodies 2 for a cutting edge preparation, the apparatus 1 may also be extended by making use of measuring technology or of sensorics. Introducing electrical conductor paths and sensors into the exchangeable holder 4 even permits an implementation of an electronical, accumulator-equipped surveillance electronics arrangement, which may be charged with a suitable charging technology in the grinding disk magazine or externally while not in use.

Due to the integration of the apparatus 1 in the grinding disk receptacle 3, only insignificantly higher acquisition costs will be incurred in comparison to customary grinding disk receptacles 3. This also means that due to the integration in the grinding disk receptacle 3, the concept is applicable on almost any tool grinding machine or processing machine. Therefore the investment—necessary for most of already known methods—for additional installations including the thus arising maintenance and repair costs, as well as for the handling of the workpiece after the grinding process. While the complete processing, for example on the tool grinding machine, causes times when the machine cannot be used for its primary purpose, such times are negligible due to the very short processing periods of less than 5 s for each preparation. Changing of tools is avoidable by an intelligent composition of grinding disk packages on the grinding mandrel and/or by furnishing each grinding disk receptacle 3 with the apparatus 1 according to the invention, resulting in an overall increase in productivity and in a considerable reduction of production costs.

The adaptation of the grinding bodies 2 to the diameter of the cutting tools 5 and the pre-defined maximum allowance of the grinding body 2 that is to be machined ensure a nearly non-relevant influencing of the cutter corners and of the secondary cutters of the cutting tools 5. Moreover, as the contact area between the cutting tool 5 and the grinding body 2 that is to be machined is limited by the machining thickness, there will be no influencing of the peripheral surfaces of the cutting tool 5. The defined length of the rotationally symmetrical grinding body 2 within the exchangeable holder 4 allows processing a number of cutting tools 5 that depends on a diameter and on a target rounding by using the proposed concept until the grinding body 2 that is to be machined is used up completely. Exchanging the exchangeable holder 4, respectively changing to a further grinding disk receptacle 3 comprising an identical grinding body 2, allows continuous processing close to the process chain. The free cinematic provided by the mounting in the grinding disk receptacle 3 also offers the potential of realizing a different process cinematic, similar to milling, on the tool grinding machine. Thus opportunities arise of preparing main cutters and secondary cutters of the cutting tools 5 with different cutting edge roundings and form factors.

In addition to the variation of the shape of the grinding bodies 2 and of the bonding hardness, it is possible to create different shapes of cutting edge rounding via an adaptation of the cinematic engagement conditions. Herein the rotation direction of the cutting tool 5, the rotation direction of the grinding body 2, the dwell time at the bottom of the bore and the advancement per turn are of particular relevance.

For long-projecting deep-drilling tools 13 having different diameters a guiding of the tool tip is necessary for enabling cutting edge preparation without getting the cutting tool 5 damaged. For this an adaptation of the exchangeable holder 4 is necessary. The guiding of the cutting tool 5 must be dimensioned such that the grinding body 2 coincides with the workpiece axis and the elastic bending of the cutting tool 5 is compensated. Herein the complexity of the preparation results from the requirements regarding the cutting edge. In the case of an application with deep-hole drilling tools, besides the more extensive rounding of the outer cutter, a significantly smaller rounding of the inner cutter must be achieved.

LIST OF REFERENCE NUMERALS

-   1 apparatus according to the invention -   2 grinding body -   3 receiving collar/grind disk receptacle -   4 exchangeable holder -   5 cutting tool -   6 thread of exchangeable holder -   7 cutters of cutting tool -   8 clamping thread -   9 clamping nut -   10 tool cone -   11 bore in grinding disk receptacle -   12 guide bushing -   13 deep hole drill -   14 grinding disk -   15 perforation -   16 core having higher bonding hardness -   17 circumferential region having lower -   bonding hardness -   18 frictional tool -   19 sequential drill -   20 milling tool -   21 surrounding grinding body -   22 inside-situated grinding body -   23 bore holder -   24 feed direction -   25 pallet-like magazine -   26 receptacles 

1. An apparatus (1) fora cutting edge preparation of cutting tools (5), wherein during a relative movement the cutting tool (5) interacts in a machining fashion with a flexibly-bonded grinding body (2) that is provided with abrasive particles, the particles of the grinding body (2) influencing the edge geometry of the cutting tool (5), wherein the grinding body (2) is adapted with its dimensions substantially to the dimensions of the respective cutting tool (5) that is to be prepared and is accommodated in an exchangeable holder (4) which is arranged in a region of a processing device and is held such that it is machinable by the cutting tool (5) for the cutting edge preparation.
 2. The apparatus (1) according to claim 1, wherein the exchangeable holder (4) is held in the workroom of a tool grinding machine.
 3. The apparatus (1) according to claim 1, wherein the grinding body (2) is implemented substantially in a cylindrical fashion.
 4. The apparatus (1) according to claim 3, wherein the cylindrical circumferential measurements of the grinding body (2) are substantially adapted to the circumferential measurements of the cutting tool (5) that is to be prepared.
 5. The apparatus (1) according claim 1, wherein after complete usage, the grinding body (2) can be simply replaced by a new grinding body (2).
 6. The apparatus (1) according to claim 1, whrerein the rotationally symmetrical grinding body (2) can be manufactured and be pressed into the exchangeable holder (4) with a very slight allowance that is adapted to the diameter of the cutting tool (5) that is to be prepared.
 7. The apparatus (1) according to claim 1, wherein the exchangeable holder (4) is insertable into a bore (11) in the grinding disk receptacle (3).
 8. The apparatus (1) according to claim 7, wherein the exchangeable holder (4) comprises an outer thread (6), which can be screwed into the bore (11) in the grinding disk receptacle (3) that is provided with an inner thread, or of a different processing device.
 9. The apparatus (1) according to claim 7, wherein that the exchangeable holder (4) can be pressed or inserted into the bore (11) in the grinding disk receptacle (3) and is held there in a rotationally fix fashion.
 10. The apparatus (1) according to claim 1, wherein a guide bushing (12) is arranged in the region of the exchangeable holder (4) for the grinding body (2), via which long-projecting asymmetrical cutting tools (13), having a great length:diameter ratio, can be guided and prepared, wherein the guide bushing (12) is arranged relative to the exchangeable holder (4) in such a way that the guide bushing (12) guides and supports the long-projecting cutting tool (13) in front of the region of the machining of the grinding body (2).
 11. The apparatus (1) according to claim 1, wherein sensor elements, which provide information on the progression of the cutting edge preparation, are introducible in the exchangeable holder (4), wherein the sensor elements are equipped with accumulators, which are integrated in the exchangeable holder (4) and can be charged in the grinding disk magazine or externally while not in use.
 12. The apparatus (1) according to claim 1, wherein the grinding body (2) comprises abrasive particles and is successively completely machinable by the cutting tools (5) which are to be prepared.
 13. The apparatus (1) according to claim 12, wherein the grinding body (2) comprises a mixture of fine and coarse abrasive particles, wherein a distribution of fine and coarse abrasive particles within the grinding body (2) is implemented inhomogeneously.
 14. The apparatus (1) according to claim 1, wherein the grinding body (2) has an axially-extending perforation (15) which is adapted to the cutting tool diameter (5) and within which the cutting tool (5) is not affected by the particles of the grinding body (2).
 15. The apparatus (1) according to claim 1, wherein the grinding body (2) comprises sections (21, 22) having differing degrees of hardness of the bonding.
 16. A method for a cutting edge preparation of cutting tools (5), wherein during a relative movement the cutting tool (5) interacts in a machining fashion with a flexibly-bonded grinding body (2) which is provided with abrasive particles, the particles of the grinding body (2) influencing the edge geometry of the cutting tool (5), wherein the grinding body (2) is adapted with its dimensions substantially to the dimensions of the respective cutting tool (5) that is to be prepared and is accommodated in an exchangeable holder (4) which is arranged in the region of a processing device and in which the grinding body (2) is successively completely machined by the cutting tools (5) which are to be prepared.
 17. The method according to claim 16, wherein the cutting edge preparation is carried out in the same clamping arrangement, directly following a first-time manufacturing of the shape of the cutting tool (5) or following a regrinding of the cutting tool (5), on the same processing device.
 18. The method according to one of claim 16, wherein in the machining of the grinding body a wide range of adaptation of the cutting speeds is obtainable by the relative movement of grinding body (2) and cutting tool (5).
 19. The method according to claim 18, wherein the grinding body (2) and the cutting tool (5) execute rotary movements during the machining of the grinding body (2), wherein a superimposition of the rotary movements of the grinding body (2) and of the cutting tool (5) permits selective roundings of the cutting edge of the cutting tool (5).
 20. The method according to claim 18, wherein during the cutting edge preparation the cutting tool (5) that is to be prepared executes the necessary translational and rotary movements.
 21. The method according to claim 16, wherein the grinding body (2) creates variable roundings over the cutting region of the cutting tools (5) by means of sections having different degrees of hardness of the bonding.
 22. The method according to claim 16, wherein due to an axially-extending perforation (15), which is adapted to the cutting tool diameter (5) and within which the cutting tool (5) is not affected by the particles of the grinding body (2), the grinding body (2) does not subject the axial regions of the cutting tool (5) to a cutting edge preparation.
 23. The method according to claim 16, wherein the grinding body (2) has external measurements which are adapted to the cutting tool diameter (5), such that only selected regions of the cutters of the cutting tool (5) are subjected to a cutting edge preparation.
 24. The method according to claim 16, wherein the cutting edge preparation is carried out on new tools (5) or on cutting tools (5) which were reground and are therefore already coated with a hard-metal layer on certain functional surfaces.
 25. The method according to claim 16, wherein the cutting tool (5) having main cutters and secondary cutters successively machines—by means of its main cutters, respectively secondary cutters—respectively corresponding grinding bodies (2) which have different characteristics and are allocated one by one.
 26. A grinding body (2) for an execution of the method according to claim 16, wherein the cylindrical circumferential measurements of the grinding body (2) are substantially adapted to the circumferential measurements of the cutting tool (5) that is to be prepared. 